Eastern Pacific Hurricane Watch Report

Report for 18 July 2016 There has been a flurry of tropical cyclones generated in the Eastern Pacific since my last Watch Report, and as most early season storms they moved west into the open Pacific and to date, none have made landfall anywhere. Since July 2nd the Eastern Pacific saw Tropical Storm Agatha, Major Hurricane Blas, and Hurricane Celia, along with currently active Hurricane Darby and Tropical Storm Estelle. These five storms in quick succession put are right on track for the average number of named systems at this point in the season, despite a quiet May and June.  Storm intensities have also proven to be just about normal with just one Major Hurricane.

There is weak to moderate mid-level flow to the west from the central Mexican mainland that has moved all of the early season storms to the west and we haven’t even seen showers related to a tropical system yet this season. 

Madden-Julian Oscillation
The MJO began an enhanced convective phase about the first of July, along with a number of incoming tropical waves from the deserts of Africa; the Eastern Pacific has been active, with two active systems at a time for the last two weeks. Forecasts call for the Madden-Julian enhanced convective phase to increase into the end of this week, with the greatest intensity along the southern coast of Mexico. The longer range forecasts call for this enhanced convection to continue to build into August. Thus the Madden-Julian component of the forecast points toward more storm formation in quick succession into the last week of the month of July. This is surmised from the 7/11/16 data release that for today 7/18, is overdue at the time of this article. 

The Sea Surface Temperatures
Of greatest significance to the strategic forecast is that the bulk of the east Eastern Pacific is 1° to 3°C over temperatures norms. This puts more potential energy in the sea’s surface to fuel tropical cyclones. 

Then there is that all important 26°C thermocline has begun to wrap around the tip of the peninsula and move up the west coast of Baja California Sur, every so slightly. The 26°C sea surface temperature is important because tropical cyclones need at least water of that temperature to sustain or build cyclonic energy. Although 26°C waters are the minimum to sustain this action, a tropical cyclone can ‘coast’ if you will once it enters sub 26°C waters. Once 26°C waters reach our shores it begins the season where the peninsula COULD suffer a significant tropical cyclone impact. 

Tropical Waves
Tropical waves are supercharged rolling areas of disturbed air, emanating from the deserts of Africa and traveling west along the ITCZ or Monsoonal Trough. There has been a flurry of them since the second of July and 5 of them resulted in a named system forming in the Eastern Pacific. Right now there are three in the pipeline from the Sahara. The first wave is entering the east Eastern Pacific today and will work westward over the next 3-5 days seeing what it can stir up and as of this afternoon, the NHC is giving that wave a 60% chance of spawning a tropical cyclone. But it is working moisture south of 10°N and tropical cyclones need to be at least north of 8.5°N to gather enough rotational energy from the Coriolis Effect. So the chances of this and another more westerly system remain low for the immediate future. 

But both of these new tropical waves are traveling further north than their predecessors, so our season is still coming.

Wind patterns
As influenced by the MJO, a weak easterly anomaly is forecast to continue another week or so. But by late in the month wind currents will lax and we’ll be counting on the counter-clockwise rotation of tropical cyclones to roll them out into the Pacific. It should be a couple more weeks after that before upper-level currents begin to move to the northeast, and put the southern peninsula under greater threat.

Surface Chart
High pressure and the presence of early season wind patterns persists well south of the peninsula. Monsoonal moisture is beginning to work west overnight, almost reaching the eastern shores of the southern portions of the peninsula. With the threat of rain from this flow showing potential to initiate thunderstorms by the weekend of the 23rd of July. With increasing humidity, the winds will begin to slacken and it will be another sign we are moving toward our tropical cyclone threat season. 

Traditionally, the threat to the peninsula begins about the middle of August. However, last year saw the earliest landfall of a named system in early June. The threat to the peninsula lasts through mid-October.

So what are we looking at in the two weeks ahead?
I had considered taking this report to weekly instead of bi-monthly by this point in July. But things have remained relatively distant from the peninsula through this month so I’ll be back with the next report at the end of July or if weather patterns begin to shift to our disfavor. 

I think the two weeks ahead are going show increasing activity, perhaps the crescendo of this season. By the 20th the southern coast of Mexico should spawn a tropical cyclone that is likely to move closer to us, more directly toward the Socorro Islands. With warm water along that path, it is likely to have at least one of the upcoming storms be a Major Hurricane.

This may sound like a ‘safe bet’ forecast, but with all the indicators pointing toward conditions conducive for tropical cyclone development it should be hard to go wrong with a forecast for a busy two weeks ahead. But what do I know… we’ll look again at the end of July.